An air filter designed to remove particulate is generally a device composed of fibrous materials. These fibrous materials may remove solid particulates such as dust, pollen, mold, and bacteria from the air. Air filters are used in applications where air quality is important, notably in building ventilation systems and in automobile engines.
Air filters may be used in automobiles, trucks, tractors, locomotives and other vehicles that use internal combustion engines. Air filters may be used with gasoline engines, diesel engines, or other engines that run on fossil fuels or other combustible substances. Air filters may be used with engines in which combustion is intermittent, such as four-stroke and two-stroke piston engines, as well as other types of engines that take in air so as to burn a combustible substance. For example, air filters may be used with some gas turbines. Filters may also be used with air compressors or in other devices that take in air.
Filters may be made from pleated paper, foam, cotton, spun fiberglass, or other known filter materials. Generally, the air intakes of internal combustion engines and compressors tend to use paper, foam, or cotton filters. Some filters use an oil bath. Air filters for internal combustion engines prevents abrasive particulate matter from entering the engine's cylinders, where it would cause mechanical wear and oil contamination.
A drawback to paper air filters is that they must be thick, or the fibers must be tightly compressed and dense, which makes paper filters restrictive to air flow. Moreover, as a paper filter becomes more and more clogged with contaminants, the pressure inside the filter drops while the atmospheric air pressure outside the filter remains the same. When the pressure differential becomes too great, due to clogging, contaminants may be pulled through the restricted air filter into the engine. Thus, the performance of a paper air filter (i.e. air flow through the filter and its ability to protect the engine) decreases over the course of the filter's service life.
As will be appreciated by those skilled in the art, one way to reduce the clogging tendency of an air filter is by using a filter material having larger openings between the various fibers comprising the filter material. Of course, a more porous filter material may allow smaller particulate matter to pass through the air filter material, unless the fibers comprising the filter material are sufficiently tacky to cause smaller contaminants to cling to the fibers rather than passing through the air filter. Various oils are known to attract airborne contaminants. However, an oil suitable for use with an air filter must be relatively non-reactive, have an excellent oxidation stability, possess good thermal stability, and retain suitable viscosity at high operating temperatures typical of automobile engines. What is needed, therefore, is a suitably formulated filter oil composition for causing tackiness throughout the air filter material so as to enhance filtration of intake air to an automobile engine.